Aquifers are generally characterized within a subterranean formation as a water table at some level below the ground surface with a capillary fringe region of varying depth overlying the water table. A vadose zone or unsaturated area typically extends between the capillary fringe and the ground surface.
Aquifers which have become contaminated such as by the presence of gasoline and other organic contaminants floating on the water table are often remediated by removing the groundwater from the aquifer and stripping contaminants from the groundwater which is then returned to the aquifer substantially free of contaminants. The use of downhole pneumatic pumps to accomplish removal of groundwater and contaminants is desirable since pneumatic pumps are generally less expensive, easier to operate and maintain and they eliminate the use of electricity and the sparking hazards associated therewith. However, conventional downhole pneumatic pumps have several disadvantages which limit their usefulness in many applications. For example, the fill rate of the pump is limited by the pressure or head of the liquid at the pump intake. To provide an acceptable fill rate, it is generally necessary to submerge the intake to a depth considerably below the liquid level in the casing and this limits the rate of floating hydrocarbon which is drawn in with the water. Also, as the liquid level fluctuates due to various influences, the position of the intake must be constantly adjusted.
Accordingly it is an object of the invention to provide an improved system for recovering groundwater.
Another object of the invention is to provide an pneumatic system for removing groundwater contaminated with hydrocarbons from a subterranean aquifer.
Still another object of the invention is to provide a pneumatic pump system which enables manipulation of the fill rate of the pump chamber independent of the depth of the pump intake below the water table.
An additional object of the invention is to provide a system of the character described which enables the removal of groundwater and organic contaminants from a subterranean formation at an increased rate as compared with conventional pneumatic systems.
Yet another object of the invention is to provide a system of the character described which enables the pump chamber of a pneumatic pump to be filled at a rate sufficient to maintain a drawdown of the water level to the pump intake to enable capture of floating contaminants.
Yet another object of the present invention is to provide a system of the character described which overcomes disadvantages of prior art pneumatic extraction systems.
Still another object of the invention is to provide a system of the character described which is uncomplicated in configuration and economical to operate.